1. Field of the Invention
The present invention relates to a vehicle vibration control system, and more specifically to a system for reducing vehicle body vibration generated by an engine.
2. Description of the Prior Art
An example of vehicle vibration control apparatus is disclosed in Japanese Published Unexamined (Kokai) Patent Appli. No. 61-207213, which comprises a vibration sensor for detecting engine or vehicle vibration; an actuator provided with a movable mass body and attached to a vehicle body via an elastic member to damp vehicle vibration; a control unit for actuating the actuator on the basis of vibration sensor signals; and a travel condition sensor. In the prior-art apparatus, the control unit commands the actuator to pass ac current through a coil to vibrate the movable mass body when the travel condition sensor detects that the vehicle is at halt, but to pass dc current through the coil to fix the movable mass body when the same sensor detects that the vehicle is travelling. Therefore, when the vehicle is at halt, since the actuator is driven by ac current, a vibration damping force corresponding to an inertia force of the movable mass body is generated and applied to the vehicle body in such a way as to cancel disturbance of torque fluctuations applied from the engine to the vehicle body or to reduce vehicle vibration. Further, when the vehicle is travelling, since the actuator is driven by dc current, the movable mass body is fixedly biased against on inner wall of the actuator by a static magnetic force generated by the dc current.
In the above-mentioned prior-art vehicle vibration control apparatus, since a large mass of about 3 to 5% of the vehicle weight is required as the movable mass body in order to effectively cancel the vehicle body vibration, there exists a problem in that the vehicle weight increases. In addition, since the vehicle vibration frequency band is composed of a plurality of frequency modes, it is impossible to effectively damp vehicle vibration by only a single actuator.
In this connection, here, an example of prior art spring constant adjustable engine mounting devices (referred to as engine mount) will be described hereinbelow with reference to FIG. 11, because these engine mounts are incorporated in the vehicle vibration control system according to the present invention.
An engine mount 3 is composed of an inner cylinder 12, an outer cylinder 14 and an elastic (rubber) body 16 interposed between these two cylinders 12 and 14. The inner cylinder 12 is attached to a vehicle body and the outer cylinder 14 is attached to an engine or vice versa to support static engine weight by the vehicle body via the elastic body 16.
The inner circumferential surface of the elastic body 16 is fixed to the inner cylinder 12, and the outer circumferential surface thereof is pressure fitted to the outer cylinder 14 via a thin rubber cylindrical member 18 fixed to the inner circumferential surface of the outer cylinder 14.
A main fluid chamber 20 and an auxiliary fluid chamber 24 are formed in the elastic body 16 with the inner cylinder 12 as a border. Further, a diaphragm 22 is formed between the auxiliary fluid chamber 24 and an inner space S of the elastic body 16 to absorb volumetric change in fluid.
A pair of opposing arcuate members 26 extending in the axial direction of the elastic body 16 are attached to the outer circumferential portion of the elastic body 16, and a cylindrical orifice forming member 28 is fitted to the thin rubber cylindrical member 18, so that a pair of orifice passages 30 and 32 can be formed between the two arcuate members 26 and the orifice forming member 28, respectively. The main fluid chamber 20 communicates with the two orifice passages 30 and 32 via two opening portions 30a and 32a and the auxiliary fluid chamber 24 communicates with the two orifice passages 30 and 32 via two other opening portions 30b and 32b.
A pair of electrode plates 34 (+) and 34a (GND) are fixed onto the arcuate member 28 and the orifice forming member 28, respectively so as to be opposed to each other within the orifice passage 30, and a pair of electrode plates 38 (+) and 36a (GND) are fixed onto the arcuate member 26 and the orifice forming member 28, respectively so as to be opposed to each other within the orifice passage 32. Further, an electro-theology fluid fills the main and auxiliary chambers 20 and 24 and the two orifice passages 30 and 32. The viscosity of the electro-rheology fluid changes according to the magnitude of electric field applied between the two pairs of opposing electrodes 34 and 34a, 36 and 36a. Therefore, the spring constant determined by the elasticity of the elastic body 16 and the viscosity of the electro-theology fluid is adjusted according to the voltage applied to the two pairs of electrodes. The above-mentioned spring constant adjustable engine mount is disclosed in Japanese Published Unexamined Utility Model Appli. No. 63-132411 in further detail, which is thereby incorporated by reference herein.